October 9, 1896.] 



SCIENCE. 



527 



bined with equal precision, has probably 

 never before been made. 



Two theodolites were employed : An 

 eighteen-inch by Troughton & Simms, and 

 a ten-inch by Repsold. Dr. Gill reaches 

 the following conclusions with regard to 

 these two instruments : 



1. That the employment of instruments 

 larger and heavier than the Eepsold ten- 

 inch is attended with no advantage. 



2. That observations should be made at 

 each station equallj'^ in the morning and 

 afternoon ; if possible, also, in opposite 

 directions of the wind. 



3. That hardened steel pivots are essen- 

 tial. 



4. That a watch telescope attached to 

 the arms of the circle microscopes not only 

 increases very materially the accuracy of 

 the observations (even when the most rigid 

 stand is employed), but it permits the use 

 of a form of stand which is easy to erect 

 and light and convenient for transport, 

 without risk of diminished accuracy. 



Many American geodesists will be sur- 

 prised by conclusions 3 and 4. 



Dr. Gill gives an interesting table of the 

 probable error of a single angle, as obtained 

 in various series of geodetic operations. 

 Some of the values given are as follows : 



No. of Prob. 

 Triangles. Error. 



South Africa, verification of Natal base, 5 ±.14 

 South Africa, prolongation of Port 



Elizabeth base, 24 .23 

 TJ. S. Coast Survey, San Francisco and 



Salt Lake, 31 .25 



U. S. Coast Survey, flat country, 198 .79 



Ordnance Survey of Great Britain, 476 1.19 



It is interesting to note that the poorest 

 work was done on the Ordnance Survey of 

 Great Britain, according to Dr. Gill's table. 



In Colonel Morris's report we find the 

 following interesting statement concerning 

 transport : 



'' The equipment of the observing part of 

 the detachment consisted of : 



1. A military ambulance wagon, drawn 

 by 16 oxen. 



2. An 18-foot buck-wagon, drawn by 16 

 oxen. 



3. A Scotch cart, drawn by six oxen. 



4. A water cart, drawn sometimes by 

 two oxen, sometimes by four. 



5. The four out-parties were each pro- 

 vided with a Scotch cart drawn by six oxen. 



The minimum number of oxen was there- 

 fore 66. A few additional animals were, 

 however, always kept to supply the place 

 of those which tired or fell sick, or which 

 died from one cause or another." 



We strongly recommend anyone in- 

 terested in geodesy to procure a copy of 

 Dr. Gill's interesting and important work. 



The Astronomische Nachrichten of September 

 8th contains an article by Dr. J. Eepsold, in 

 which he describes the newest micrometer 

 devised by his firm. It is an instrument 

 intended to combine the new form of tran- 

 sit micrometer, in which an effort was made 

 to avoid the effects of personal equation, 

 with a new kind of registering declination 

 micrometer. Dr. Repsold points out that 

 it is very desirable to increase the precision 

 with which declination bisections can be 

 made in the field of view, so as to bring the 

 bisection to the same order of accuracy at- 

 tainable in the reading of the circle micro- 

 scopes. H. J. 



NOTES ON INORGANIC CHEMISTBY. 



In the current Comptes Rendus P. Villard 

 describes a crystallized hydrate of argon 

 with water. Argon is compressed to 150 

 atmospheres in the presence of water cooled 

 to nearly zero. On chilling the tube at a 

 small point crystallization begins proceed- 

 ing out from the point cooled. Or crystalli- 

 zation may be induced by introducing a 

 crystal of the hydrate previously formed. 

 Crystallization does not take place, however, 

 by merely compressing argon in the pres- 



